Fluoride Evaporation of Low-Fluoride CaF(2)-CaO-Al(2)O(3)-MgO-TiO(2)-(Na(2)O-K(2)O) Slag for Electroslag Remelting

To elucidate the behavior of fluoride evaporation in an electroslag remelting process, the non-isothermal evaporation of the low-fluoride CaF(2)-CaO-Al(2)O(3)-MgO-TiO(2)-(Na(2)O-K(2)O) slag is studied using thermogravimetric analysis. The evaporation law of the melted slag is further verified using thermodynamic calculations. Fourier transformation infrared (FTIR) spectroscopy is used to evaluate the change in slag structure. It is discovered that the principal evaporating substances are CaF(2), KF, and NaF, while the evaporation of MgF(2), AlF(3), and AlOF is less. KF evaporates absolutely in the early stage of the reaction, and CaF(2) evaporates in a large proportion during the late reaction period. At 1500 °C, the order of vapor pressure is KF > CaF(2). When K(2)O and Na(2)O are added to the residue sample at the same time, the evaporation ability of KF is stronger than that of CaF(2) and NaF. As the K(2)O content increases from 0 to 8.3 wt%, evaporation increases from 0.76% to 1.21%. The evaporation rates of samples containing more K(2)O and those containing more Na(2)O are 1.48% and 1.32%, respectively. Under the same conditions, K(2)O has a greater effect on evaporation than Na(2)O. FTIR results show that the addition of K(2)O depolymerizes the network structure and that K(2)O can depolymerize the network structure better than Na(2)O.